Methods for Characterization of Batteries Using Acoustic Interrogation

Abstract
Batteries are a ubiquitous form of electrochemical energy storage, but thus far the methods for measuring the mechanical properties of batteries and their component materials during operation have lagged far behind the methods for measuring the corresponding electrical properties. In this work, I demonstrate methods for determining the changes in material properties of a battery both during and after operation.
I begin by establishing the how, in an alkaline AA battery, changes in the materials at the micro-scale can affect the mechanical behavior of the entire cell. This is demonstrated using a bounce test, in which the bounce height of the alkaline battery is shown to depend on the remaining capacity of the battery. This occurs because of the way in which the Zn-gel anode at the center of the battery solidifies during use.
Building from this, I present a generalized solution for materials characterization in batteries during operation using ultrasonic pulses. The material properties of battery components change during charge and discharge, resulting in a change in how quickly the pulse can propagate through the components. By attaching transducers to a battery during cycling and sending ultrasonic pulses through each cell, I observe the changes in the transit time of the pulses, both in reflection and transmission. I show that these changes correspond to both remaining capacity and the health of the cell in a variety of battery chemistries and geometries, and detail a corresponding computational model.
Finally, I use the presented method to perform characterization of commercially available alkaline AA batteries. By correlating these results with other characterization methods, I show that our method is capable of determining the previously mentioned morphology changes due to utilization and solidification of the anode. I also show that our method can determine differences in the quality of component materials between multiple alkaline AA battery brands.